It is known to implant a coded transponder in farm animals (see for example EP 0,299,557 NEDAP). A transponder is capable of generating an identification signal, e.g. a code, in response to an electromagnetic interrogation field generated by a transmitter/receiver. However an implanted transponder may migrate in the animal, either as the whole transponder or as fragments thereof resulting from breakage of the transponder. At the time of slaughtering it is desirable that each transponder is accounted for, so that misuse is prevented and the risk of migration or loss is overcome. However it is very difficult to recover all implanted transponders, particularly because of the rapid movement of the animals or their carcases in a slaughter house so that there may be insufficient time to retrieve the transponders. There is a risk that a transponder, or residues thereof, may enter the food chain. Furthermore such a transponder does not provide identification of the animal in situations where the appropriate interrogation unit is not available.
In our International Patent Application WO91/10982 we have described an animal ear tag having a cylindrical transponder in a chamber inside the male part of the tag. An identification index encoded in the transponder is also represented visually on the tag. However ear tags are regarded by some Authorities as less than satisfactory because of a risk of damage or loss from external contact or tampering. While we do not agree with this view, we have now investigated other alternative identification systems.
U.S. Pat. No. 4,262,632 Hanton et. al. describes an electronic identification system for ruminant animals comprising a transmitter capsule precoded to broadcast a series of binary coded electric pulses peculiar to the animal, the transmitter capsule being designed by adjusting its specific gravity to reside permanently in the animal's second stomach or reticulum. The electronics are encapsulated in a housing of a material which can be accepted physiologically by the animal and yet not be attacked by the other contents in the animal's reticulum. The specification indicates that capsules with specific gravities of approximately 1.7 or greater have been successfully retained and that permanent retention is assured with specific gravities of 2 or greater. In the illustrated embodiment, the electronics and a weight are inserted in a glass housing and the capsule is then evacuated and sealed off. Quartz and fiberglass are also mentioned as suitable materials for the housing.
GB 2,165,723A describes an animal identification device comprising a transponder in the form of an electronically coded bolus which fits inside the animal's reticulum. The components of the transponder are encoded in a cylindrical tube of hard, clear plastics material.
ZA 8,303,599-A discloses an identification system for animals with primary and secondary stomachs which uses a radio transmitter located in the primary stomach and which is coded to identify the animal. The transmitter housing may be an inert plastics material.
The foregoing "bolus" identification systems require the presence of a suitable interrogation unit in order to identify an animal. There is therefore a problem in identifying an animal if death or slaughter takes place in circumstances when no interrogation unit is available, for example on a farm, during transit or on occasions when an interrogation unit may be inoperative for some reason. There may also be a problem if the electronic identification device malfunctions or becomes inoperative during a long period of residence of the bolus in an animal's stomach. When an electronic identification device encodes a particular identification code, it has an electronic state which is different from that of any other device encoding a different identification code. If no interrogation unit is available, there is no means of indicating the electronic state of the device. Likewise if the identification device malfunctions or becomes inoperative, there is no means of indicating the former electronic state of the device. This is a different problem than would be encountered with an ear tag which is accessible and available for inspection throughout the animal's life and which can be readily replaced if necessary. It is also desirable that an identification code held in the electronic device should also be readily useable in record systems relating to the animal, either computer systems or "hard copy" systems such as record cards, health certificates and the like.
While electronic animal identification systems are particularly intended for use in control of animal diseases and/or for herd management, they do not however themselves provide any indication of animals which are suffering from disease or which are in a particular physical condition, such as the onset of oestrus.
To this end, it has been proposed to monitor body temperature changes in cows by measuring the temperature of milk as it comes from the cow. However this technique has disadvantages e.g. the temperature readings are subject to external influences, there is a lengthy interval between milkings, and a difficulty of comparison with previous readings.
Joseph Pfistershammer of C.I.C. Enterprises P/L, Perth, Western Australia, has proposed a removable intra-vaginal thermosensing device to monitor the variations of a cow's body heat, particularly for oestrus detection. Electronic data gathered by the monitor in the vaginal insert is relayed to a stationary receiver at least once in every 24 hours and software in the controlling unit is programmed to interpret the information, distinguishing between normal and abnormal temperature variations, including those that indicate the onset of a disease or a likely pregnancy. However Pfistershammer only suggests retention of the electronic device within the vagina for some 3 months.
EP 0,395,188 NEDAP describes a probe comprising a digital code circuit in which an identification code is stored, as well as a substantially digital measuring circuit connected to a temperature sensor element.
It is a further object of the present invention to provide a system for monitoring body temperature for substantially the whole life of an animal.